You know, I've had the same problems finding the information, but it really changes nothing in terms of PHP. Look for general articles on setting up SSL and getting a certificate from a recognised ceritifer, and then you'll simply have either a new FTP, or a separate directory on your FTP which is for the secure files, so then you'll have the HTTP version and HTTPS.

Therefore when you want to use the secure SSL, link to the files on the HTTPS. The only real difference in terms of PHP is that you'll want to check for the protocol being used - HTTP or HTTPS. This prevents secure pages being used without the secure protocol.

As SSL is quite expensive in terms of the bandwidth being utilised to first setting up a encryption system, a lot of websites load the main chuck of the page in HTTP and then embed the login boxes in HTTPS. If you remember, there used to be a warning in Internet Explorer, and still is, where it informs you that there are both secure and insecure elements on the page. That happens for that very reason because of HTTP and HTTPS on one page.

__________________
The man who comes back through the Door in the Wall will never be quite the same as the man who went out.